As an alternative to shaving, many hair removal products available today perform through either chemical degradation (depilation) or mechanical removal (epilation) of the hair. Compositions for removing superfluous body hair are well known and are of various types. Currently on the market there are many different types of chemical depilatories and epilation products. Epilatory products, such as waxing, require initial heating before being applied to the skin in a generally molten state. It is then allowed to solidify before being removed from the skin together with unwanted hair.
One major drawback with waxing is the pain associated with hair removal. Waxing works by pulling the hair out from the roots. The hair follicle is surrounded by a small muscle that allows the hair to be erected in response to cold or excitement. Also attached with this muscle are nerve endings.
These structures make pulling the hair out fairly hard and painful. The pain creates a fear associated with the waxing procedure which will cause many people not to repeat the procedure. Even if the person does repeat the waxing, the fear can cause the muscles to tense up, which in turn creates even more pain in subsequent procedures.
Chemical-based depilation offers an attractive alternative to waxing or shaving with the removal of hair being accomplished through the cleavage of disulfide bonds in the hair fiber as well as denaturation of the associated protein matrix. Unlike waxing, chemical-based depilation digests the hair and the hair is not pulled out, thus avoiding the pain associated with waxing. However, a relatively small proportion of individuals, compared with shaving, employ depilatories. One reason for the limited use may be that the hair cleavage reaction must be run at a very high pH. A typical example is the Nair® lotion product, having a pH of about 12.5 to 13.
Chemical-based depilatory compositions typically use a thiol-based depilatory agent, such as thioglycolic acid, for removal of unwanted body and facial hair and its use is well established in the art. These agents react by reducing hair's protein disulfide bonds to sulfhydryl anions, thereby allowing easy removal of the weakened hairs when washed or wiped away. However, in using thiols, it was discovered that certain conditions facilitated the effectiveness of this reaction. One such condition is high alkalinity to provide ionized reactants. Not only does the high pH (approximately 12.0-13) result in ionized thiols, but they also result in increased penetration of a reactant. Substances to provide further enhancement of penetration by active thiols were developed.
Currently on the market there are many different types of chemical depilatories. They range in form from creams to gel to aerosol mousses and spray products. Depilatory composition in the form of a cream is applied to the skin at room temperature. One drawback to many of these depilatory products is the required clean up. As discussed earlier, chemical depilatories contain a strong alkaline, usually a metal hydroxide. In addition, there is usually a reducing agent used. These chemicals can cause considerable damage to the skin if not properly removed. Likewise, they will quickly cause significant damage if they get into the eyes. Product wiped off the skin is still active and will corrode aluminum and many organic materials, creating the possibility of property damage or injury to the user, children or pets through inadvertent contact.
Products have been made to help reduce the risks associated with using these high pH depilatory products by trapping the dangerous chemicals in a solid matrix, i.e., a semi-solid film, after use, thereby simplifying disposal because there will not be liquid which can stick to surfaces. These depilatory products form a dry rubbery film on the skin which after a period of a few minutes can be peeled in one piece from the skin. In this manner, the product is similar to a hot wax depilation. After removal of the product, a very slight residue is left behind, which could be removed with a damp towel. However, unlike wax, the hair will have been digested by chemicals and not pulled out, thereby avoiding the pain associated with pulling out hair as in waxing. Further, there is the elimination of a great deal of mess. European Patent Application No. 0196896A2 to Hori et al. describes such a product.
European Patent Application No. 0196896A2 describes a depilatory composition comprising an aqueous solution or emulsion (e.g. a paste or gel) of a depilatory agent, a film-forming polymer (such as poly(vinyl alcohol)), which can be water-soluble or insoluble, and optionally an alkali hair swelling accelerating agent or a filler. The composition of European Patent Application No. 0196896A2 is spread on an area of skin having hair, the coating is allowed to dry naturally or by treating with hot air and/or absorbing water into an absorbent sheet pressed onto the film; and the film is peeled off with the hairs embedded therein, optionally with use of a pressure-sensitive adhesive sheet placed on the film.
In using these depilatory compositions, it is advantageous to have compositions which are capable of forming films when they are applied to the skin. Compositions having film-forming properties have the advantages of facilitating the removal of the depilatory composition from the skin and the ease of disposal of the depilatory composition along with the digested hairs simply by peeling off the dried composition.
The components imparting the above-noted film-forming properties are generally high-molecular-weight polymers. To obtain substantial film-forming properties in depilatory compositions, it is not satisfactory to simply increase the concentration of these high-molecular-weight polymers in the depilatory compositions. Such an approach is indeed limited by the fact that these film-forming polymers excessively increase the viscosity of the finished product. The finished product becomes too thick; it is thus difficult to apply to the skin and therefore preventing the user from being able to properly apply the depilatory composition.
It would be most useful to formulate a depilatory composition with substantial film-forming properties, but in such a way that the viscosity of depilatory composition is low enough to properly apply to the skin as a thin film prior to forming a film.